As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are commercially available in sealed packages made of a packaging material that has previously been sterilised.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multi-layer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or of mineral-filled polypropylene material, and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH), which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution. Once sterilization is completed, the sterilization agent is removed from the surfaces of the packaging material, e.g. evaporated by heating. The web of packaging material sterilized in this manner is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed at equally spaced cross sections, along which it is eventually cut to form the packs. These pillow-shaped packs are then folded mechanically to form finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles. These packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
According to a possible manufacturing process a spout is injection moulded directly onto the packaging material when the packaging material has the shape of a web, or a sheet, i.e. before the packaging material is formed, filled and sealed so as to obtain the final packages.
In this case, the spout comprises a flange attached to the packaging material, a neck—for example a threaded neck—protruding from the packaging material and defining a pouring opening, and a wall closing the pouring opening and removable from the neck through a pull element that may be pulled by a user when the package is opened for the first time.
As disclosed above, the formed, filled and sealed packages come out from the filling machine with their necks extending from a top wall of the packages.
Downstream of the filling machine there is provided an applying unit for applying lids to the necks of the packages.
The applying unit comprises a conveyor along which the packages are advanced, a distribution unit that releases a lid to a respective neck, whilst the package is advanced by the conveyor, and a capping unit that screws the lid onto the neck. The capping unit comprises a couple of belts. Each belt has an active branch that is substantially parallel to the active branch of the other belt. The active branches move along opposite directions and interact with diametrically opposite portions of the lid, so as to rotate the lid and screw the lid onto the neck.
A drawback of the known applying units is that they are not very precise. The belts, in fact, may be worn so affecting the positioning of the lids and the screwing torque.
The known applying units apply the lids owing to the friction between the belts and the lids. The performances of the known applying unit, therefore, depend on the settings and on the adjustments and fine tuning carried out by the operator. The known applying units, therefore, may be not very reliable, especially when the output rate is high.
In addition, the known applying units are not very flexible. In other words, major re-arrangements are required in case the size and shape of the packages on which the lids have to be applied is changed.
Moreover, since the belts interact with diametrically opposite portions of the lid, the known applying units are only suitable for applying round, or substantially round, lids.